Following a trauma to a shoulder or a hip, such as a fracture, implantation technology may be used. In this event, the implant is inserted into a corresponding long bone, namely the humerus or the femur. This application into such bones may be carried out provisionally or definitively.
Two types of implant are currently used. The first kind relates to a definitive or trial prosthesis which makes it possible to restore the articulation. The second type of implant corresponds to an osteosynthesis device, such as a nail. The nail, an implant temporary in nature, is used especially when it is wished to maintain pieces of the fractured bone in the original anatomical position and thus to induce a bone fusion.
In the case of applying a shoulder or hip prosthesis, the surgeon must ensure anatomic and durable reconstruction, as well as correct reconstruction of the biomechanical articulation properties.
Following a fracture of a humerus or a femur, it is known to reassemble the various bone fragments by means of a humeral or femoral nail respectively. In this case, the surgeon must ensure proper consolidation of the various pieces of the fractured bone.
Conventionally, the surgeon uses, for the two types of implants, locking devices described as external. For trial or definitive prostheses a positioning ancillary is commonly used. This tool makes it possible to stabilize the prosthesis once this has been inserted into the bone. In the case of a nail, it is in particular known to use screws for joining the lower end of the nail with the lower part of the diaphysis of the bone.
However, the use of such a tool or of such screws does not make the fixing of the prosthesis or of the nail easy for the surgeon. This is because the surgeon must provide an additional operating step. The operating time will therefore naturally increase. In addition to the complexity of fitting this tool or these screws, a change in the position of the prosthesis or of the screws may appear after the fitting of the implant. This may cause pain to the patient. A new operation may optionally be reprogrammed.
In order to eliminate this drawback, locking devices described as internal have been developed. Firstly, the surgeon inserts the prosthesis into the medullary canal of the bone. Subsequently, using a drive means, the humeral or femoral stem of the prosthesis increases its diameter homogeneously and symmetrically relative to its central axis until it is able to anchor itself in the bone.
However, such a locking device is not satisfactory as it does not enable effective locking of the prosthesis in the bone. This is because the rotational stability of this device is insufficient after its employment. The anchoring in the bone is for this reason less precise.